Expandable liner hangers are generally used to secure a liner within a previously set casing or liner string. These types of liner hangers are typically set by expanding the liner hangers radially outward into gripping and sealing contact with the previous casing or liner string. Many such liner hangers are expanded by use of hydraulic pressure to drive an expanding cone or wedge through the liner hanger.
The expansion process is typically performed by means of a running tool or setting tool used to convey the liner hanger and attached liner into a wellbore. The running tool or setting tool may be interconnected between a work string (e.g., a tubular string made up of drill pipe or other segmented or continuous tubular elements) and the liner hanger.
If the liner hanger is expanded using hydraulic pressure, then the running tool or setting tool is generally used to control the communication of fluid pressure and flow to and from various portions of the liner hanger expansion mechanism, and between the work string and the liner. The running tool or setting tool also may be used to control when and how the work string is released from the liner hanger, for example, after expansion of the liner hanger or after an unsuccessful setting of the liner hanger.
The running tool or setting tool may provide for cementing therethrough, in those cases in which the liner is to be cemented in the wellbore. Some designs of the running or setting tool employ a ball or cementing plug that is dropped through the work string at the completion of the cementing operation and prior to expanding the liner hanger. However, at substantial depths and/or in highly deviated wellbores, it may take a very long time for the ball to reach the running or setting tool, during which time cement may be setting up around the drill pipe and potentially causing the drill pipe to get stuck. In addition, the ball may not reach the running or setting tool at all. Furthermore, the cementing plug may not be able to be landed correctly on a corresponding float collar.